1. Field of the Invention
This invention relates to mechanical air-fuel blending systems for highly compressed gases, such as Liquified Petroleum (LP) and, more particularly, to mechanical air-fuel system which utilizes a portion of the compressed gaseous fuel charge in its gaseous state as a control means to balance the fuel mass to the air mass in an internal combustion engine.
2. History of the Prior Art
A conventional Liquified Petroleum (LP) fuel system in use today for internal combustion engines is illustrated in U.S. Pat. No. 4,503,831 to Rijkeboer. The apparatus in Rijkeboer stores the LP gas in a liquid phase in a tank which has a working pressure of approximately 265 psig. In operation, the fuel leaves the tank and passes through a filter and a vacuum-controlled safety shutoff valve which stops the fuel flow whenever the engine is stopped.
During engine start, the fuel enters a converter, which is a two-stage pressure regulating device which converts the fuel to a gaseous state. The converter is heated with water from the engine's cooling system to supply latent heat to the fuel and to maintain the fuel at a constant temperature. The first stage of the converter reduces the fuel pressure to about 5 psig. The second stage is a demand regulator which reduces the pressure to a partial vacuum of about 1 to 2 inches of water. The fuel then moves through a suitable hose to either an air valve or a venturi adapter where the fuel is blended with the air charge before entering the engine induction system.
In addition to the two or three stage converters described above, it has also been common practice to put a heat riser ahead of the fuel injectors to increase the temperature of the incoming ambient air by about 50.degree. F., so that when the air mixes with the LP gas, the high air temperature ensures that the fuel is in a totally gaseous state when it is injected into the engine cylinders. Thus, past systems which heat the entire fuel flow to a gaseous state, have been very large and complex, and have been difficult to maintain.
Some existing systems, such as that disclosed in U.S. Pat. No. 4,503,832 to Pefley et al., increase available engine power when using a secondary fuel by maintaining the secondary fuel in a liquid state until it reaches the fuel injector. Secondary fuels contain about 30 to 40 percent less latent energy than gasoline or diesel fuel. In the gaseous state, acceptable levels of performance can still be attained at power levels up to about 85 percent of the maximum engine power which is available using gasoline. At power settings above 85 percent, however, very little additional power can be attained from gaseous secondary fuels because the air flow to the engine is restricted. Air flow is critical to engine power generation, and the air flow is restricted at power settings above 85 percent for two reasons. First, because of the reduced energy content of secondary fuels, a greater volume of fuel is required to generate the same amount of energy as gasoline. The greater volume of fuel displaces the air and reduces the power generated. Second, the additional 50.degree. F. of air temperature from the heat riser reduces the density of the air flow which can be allowed. If the heat riser is removed, a vehicle using LP gas can attain a maximum power of approximately 90 percent of that attainable with gasoline.
When LP gas is released from the pressure vessel, it creates an extreme chilling effect as it rapidly expands and returns to a gaseous state. When LP gas is delivered to the injector, such that the total expansion of the fuel takes place within the injector air stream, without a heat riser, the refrigerating effect of the expanding gas lowers the temperature of the air-fuel charge by approximately 80.degree. F. and increases the density of the air-fuel charge by approximately 18 percent. This results in an increase of approximately 63 percent in available power above the design maximum power of the engine. With LP as the fuel, and the total expansion of the LP taking place within the injector airstream, without a heat riser, the air-fuel temperature is lowered by approximately 50.degree. F. This increases the air density by approximately 7 percent, increasing the available engine power above the design maximum power by approximately 45 percent.
Although systems such as Pefley, et al. may achieve the benefits of injecting LP gas in the liquid state, they do so by utilizing complex cooling systems to maintain the LP gas as a liquid until it reaches the inlet air stream. Thus, the increased power is achieved at the expense of increased system complexity and its associated reduced reliability and increased maintenance costs.
It would be a distinct advantage to have a system which is capable of delivering liquid secondary fuels directly into the inlet air stream of an internal combustion engine, and which is small and reliable due to a simple mechanical design. The present invention provides for a very simple and compact fuel system for internal combustion engines which introduces the fuel to the air stream at storage pressures across a single fuel valve. The compact size and the absence of a water heated converter allow for a much simpler, less expensive, and more reliable installation.